This invention relates generally to devices incorporating telescoping tubes having adjustable relative lengths, and specifically to a mechanism for selectively locking the relative positions of a pair of telescoping tubes for providing a combined tubular assembly of differing lengths.
The present type of adjustable tubular assembly is found in a variety of consumer products. One such product is a medical table such as an overbed table with vertical adjustability. However, it is contemplated that the present invention may be used in other products, and is not restricted to overbed tables.
Overbed tables are widely used in hospitals, nursing homes, and the like. It is desirable that the tables be vertically adjustable in order to accommodate beds and chairs of varying heights. Typically, an overbed table consists of a pair of telescoping tubes mounted on a movable stand and having a horizontal tabletop surface mounted to one of the tubes. The height of the table is determined by the relative positions of the tubes between a retracted position and an extended position. The tubes can be locked at, and released from, numerous positions. Several mechanisms for locking a table at a selected height are known in the art.
One such locking mechanism is shown in U.S. Pat. No. 4,601,246 to Damico. This mechanism employs a wedge and roller clutch mechanism to lock a pair of vertically telescoping tubes. However, this mechanism employs two wedges and at least one and preferably two rollers and, without expensive precision manufacturing of these pieces, it is difficult to make both rollers "grab" simultaneously during adjustment of the height of the table. This results in an echo effect--the second roller grabbing after the first--while attempting to lock the table at the selected height, which tends to hinder precise adjustment of the height. Furthermore, this type of adjustment results in a rough and uneven movement of the tubes relative to each other.
U.S. Pat. Nos. 5,016,846 and 5,106,043 to Solomon provide for a cam plate type locking mechanism with a single locking plate pivotally mounted to the inner telescoping tube. To lock the inner tube to the outer tube, a spring forces this plate into contact with an interior surface of the outer tube. After repeated uses of the mechanism, the interior surface of the outer tube has numerous dents caused by the locking plate. Hence, operation of the table becomes noisy and operation of the release mechanism may require considerable force.
Accordingly, it is the primary object of the present invention to provide an improved selective locking mechanism for a pair of telescoping tubes which provides for precision adjustment of the relative position of the two tubes.
It is another object of the present invention to provide an improved overbed table with a selective locking mechanism employing a pair of telescoping tubes, the locking mechanism configured for silent and smooth adjustment of table height.
It is a further object of the present invention to provide an improved overbed table with a selective locking mechanism that is easily released.